This work deals with the development of a new tribometer designed for the characterisation of the frictional properties at the tool/chip/workpiece interfaces in cutting processes. Based on a plane-sphere contact confi guration, the experimental set-up enables a continuous regeneration of the pinworkmaterial contact. The average contact pressure can be selected up to 3 GPa under sliding velocities reaching 16 m/s. Under such severe conditions, which are not reachable with conventional tribometers, the apparent friction coeffi cient is quantifi ed in parallel to the heat fl ux transmitted to the pin. This new system has been applied to the characterisation of the frictional properties during the dry machining of a 27MnCr5 annealed steel with a carbide cutting tool. The infl uence of the sliding velocity and of an additional TiN layer deposited by PVD on the carbide pins has been investigated in dry conditions. It has been shown that the sliding velocity is the more infl uential parameter, followed by the coating.
S u m m a r yThis paper aims at characterizing the frictional behaviour at the cutting tool-workmaterial interface during the dry machining of a Inconel 718 in its aged state with various coated carbide tools and c-BN tools. A specially designed open tribometer has been used to characterize friction coefficient, heat partition coefficient under extreme conditions corresponding to the ones occurring in cutting. The tribometer provides the evolution of the apparent friction coefficient and of the heat partition coefficient for a large range of sliding velocity and contact pressure. It has been shown that friction coefficient as well as heat partition coefficient decrease with sliding velocity or contact pressure. A threshold effect of the contact pressure has been highlighted. On the contrary, any sensitivity to coatings deposited on carbide has been observed, whereas c-BN leads to very low friction coefficients. Identyfikacja tarcia i model podziału ciepła w strefie kontaktu wiór-ostrze-materiał obrabiany w toczeniu na sucho nadstopu Inconel 718 narzędziami z CBN i węglików spiekanych z naniesionymi powłokami S t r e s z c z e n i e W pracy określono charakterystykę tarciowego zachowania się strefy kontaktu wiór-ostrze obrabianego w toczeniu na sucho nadstopu Inconel 718 po starzeniu narzędziami wykonanymi z różnych gatunków węglików spiekanych z naniesionymi powłokami i polikrystalicznego CBN. Zaprojektowano i wykonano tribometr do wyznaczania wartości współczynnika tarcia i współczynnika podziału ciepła. Badania prowadzono w warunkach ekstremalnych zbliżonych do występujących w procesie skrawania na sucho. Tribometr umożliwia pomiary w czasie wartości pozornego współczynnika tarcia i przepływ ciepła dla dużego zakresu wartości prędkości skrawania i nacisku normalnego. Wykazano, że zarówno współczynnik tarcia, jak i podziału ciepła zmniejszają się przy wzroście prędkości i siły normalnej skrawania. Określono graniczny efekt nacisku kontaktowego. Nie stwierdzono wpływu rodzaju powłoki 6 F. Zemzemi, J. Rech, W. Ben Salem, A. Dogui, Ph. Kapsa na ostrzu z węglika spiekanego na wartość współczynnika tarcia. Natomiast skrawanie narzędziami z ostrzem p-CBN prowadzi do uzyskania bardzo małej wartości współczynnika tarcia. Słowa kluczowe: Inconel 718, skrawanie, tarcie, współczynnik podziału ciepła, regularny azotek boru, powłoki, węgliki spiekane Identification of friction and heat partition model ... 7
Unsuitable surface quality is frequently observed in the machining of composites due to their heterogeneity and anisotropic properties. Thus, minimizing the machining damages requires a thorough understanding of the machining process. In this study, two different finite element models were developed using Abaqus/Explicit to simulate the cutting process of unidirectional carbon fiber-reinforced polymer: (i) a macromechanical model based on the homogenization approach and (ii) a micromechanical model in which the composite constituents were treated separately. The effects of CFRP mechanical properties, the energy of breaking and hourglass control were analyzed using a macromechanical model. The results revealed that CFRP properties and the numerical parameters highly influenced the cutting process. A comparative study was also performed between the macromechanical and the micromechanical models to study the mechanisms of chip formation. It was demonstrated that the material removal mechanisms for both models are in good agreement with the experimental observations for different fiber orientation angles.
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